Hydrogen sulphide is a colorless gas, with an odor of rotten eggs. It is produced by bacterial action during the decay of both plant and animal protein and may be formed wherever elemental sulphur or certain sulphur-containing compounds come into contact with organic materials at high temperatures. In industry, it is usually an unintended byproduct, for example from the production of coke from sulphur-containing coal, from the refining of sulphur-containing crude oils, the production of disulphide, the manufacture of viscose rayon, and in the Kraft process for wood pulp.
Hydrogen sulphide is also a byproduct of wastewater from treatment plants or water from agricultural practices. Additionally, hydrogen sulphide may be responsible for the unpleasant odor from liquids used in janitorial processes, RV holding tanks, portable toilets and the like. If the emission of hydrogen sulphide from these liquids may be controlled, then the unpleasant odors may be eliminated.
Hydrogen sulphide is toxic to humans and other animals, and represents a significant threat to public safety and health. It can cause serious health risks and fatalities, most notably in the oil and gas, livestock, waste management and janitorial industries.
Natural gases and oils with high concentrations of hydrogen sulphide are known as “sour” and the hydrogen sulphide in sour gas and oil streams is separated using a “sweetening” process.
Many chemical compositions are used as absorption agents in sweetening processes; these include caustic soda, ammonia and amines. Gas and oil streams with high daily flows of hydrogen sulphide and other sulphur contaminants are typically treated in sweetening processes that, for economic reasons, regenerate the chemical solvents after they have absorbed the sulphur contaminants from the process stream. When the daily sulphur flow is low, it is usually uneconomic to employ a regenerative process and the sulphur compounds are removed with treatment chemicals know as “scavengers” which absorb hydrogen sulphide and other compounds from the process stream and bind these compounds in the “spent” scavenger which is removed to a safe disposal site.
There are many scavengers used in industry but all suffer from disadvantages.
A scavenger intended for controlling hydrogen sulphide in oil drilling is described in U.S. Pat. No. 4,147,212. While this formulation removes hydrogen sulphide from gas streams and liquid streams, when the scavenger is diluted with water, the zinc component of the scavenging agent is precipitated from solution, thereby limiting the desirability of this scavenger in many industrial applications. As a solid precipitate, the zinc component can settle out from solution and no longer have any activity within the composition.
There is a need for a simple, economical and effective means of removing sulphur compounds and carbon dioxide present in substances, while preventing the problem of precipitation from the scavenger prior to reacting with the sulphur compounds or carbon dioxide.